Method and apparatus for detecting pinholes on sheet articles

ABSTRACT

Method and apparatus for detecting pinholes and edge cracks in such sheet articles as paper, rubber sheet and metal sheets by using such detection facilities as a television camera.

United States Patent 1 1 Watanabe et al.

METHOD AND APPARATUS FOR DETECTING PINHOLES ON SHEET ARTICLES lnventors: Tetsuo Watanabe; Shinya Hashirizaki, both of Kitakyushu, Japan Assignee: Nippon Steel Corporation, Tokyo,

Japan Filedz Jan. 14, 1970 Appl. No.: 2,724

Foreign Application Priority Data Jan. 16, 1969 Japan ..44/3004 Aug. 1, 1969 Japan ..44/6l345 US. Cl ..l78/6, l78/DIG. 37 Int. Cl. ..I*I04h 7/02 Feb. 6, 1973 [58] Field of Search .....178/61 ND, DlG. 37, DlG. l"

[56] References Cited UNITED STATES PATENTS 3,379,829 4 1968 Gambrell et al. 1 78/DlG. 37 2,935,559 5/1960 Dornier ..l78/DlG. 1 3,389,789 6 1968 Watson et al. ..178 61 ND 3,390,229 6 1968 Williams ..178 61 ND Primary Examiner-Robert L. Griffin Assistant ExaminerBarry L. Leibowitz Attorney-Wenderoth, Lind & Ponack [5 7] ABSTRACT Method and apparatus for detecting pinholes and edge cracks in such sheet articles as paper, rubber sheet and metal sheets by using such detection facilities as a television camera.

9 Claims, 17 Drawing Figures APP FOR DETECTING ELEC SIG PATENTED FEB 6 I975 3,715,476 SHEET 10F 4 APP FOR DETECTING ELEC SIG AMPL 42 TV CONT SCHMIDT T UNIT CKT l CTR T4 FIG. 5 2 2| 1 I 25 (27 I I My 24 1 24 la i 28 mi I H: .T//

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:75 E8 5 5 7m o m 9 CE w 50 n r w E 6m mwwmwfim C6 is? 5.152; 555m 56 mm MEG m mi BY fill: J mmlb ATTORNEY S METHOD AND APPARATUS FOR DETECTING PINIIOLIES ON SHEET ARTICLES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting pinholes and edge cracks, in general, in thin articles, particularly in paper, rubber sheet, metal sheets, etc., by using a television camera, etc.

2. Description of the Prior Art In order to detect pinholes and edge cracks in such thin articles as thin steel sheet, there is conventionally used a method, according to which light is cast on the front surface of such steel sheet, and light which comes through to the back surface is picked up by photoelectric elements. However, this method requires a dark box, and also a means for preventing light leakage from both side edges of said sheets; because such means is used, there is an area, called a dead zone, along the respective side edges, which is not covered by said means and, therefore, cannot be examined for detection of pinholes.

As pinholes are left undetected in the dead zone, the zone is cut off and thrown away. However, economic requirements have recently emphasized the necessity of cost reduction in the production of such sheet; and even such dead zone area must be utilized, so that the detection of pinholes must be extended to this area.

But, as mentioned below, it is technically difficult to detect pinholes in such area, and no solution of this problem has been found in spite of the pressure of necessity. Besides, the method using a dark box is inconvenient and inefficient for detection of pinholes, and difficult to maintain, these complications being among many other shortcomings of the method.

SUMMARY OF THE INVENTION The inventors of the present invention have developed a method for solving the above problems, that is, a method for detecting pinholes and edge cracks in articles, according to which light is cast from the source onto one surface of an article to be examined such as metal sheets, and the other surface of said article is scanned by a television camera for picking up light coming through the sheet, which is converted into a signal to be charged into a signal selection circuit for any light which has passed through the article, thereby detecting pinholes therein.

Besides, the inventors have developed a method for detecting pinholes on the side edges of the examined article as accurately as in the other part of the article. According to this method, light is cast from a source set above one surface of the article to be examined, over a greater width than the width of the surface of the article, and the other surface of the article is scanned by a television camera for simultaneous detection of light from said light source which comes through the article to be examined, which is converted into a video signal to be charged into a gate circuit through an amplifier and a Schmidt circuit, and at the same time, to be fed from the Schmidt circuit, as setting signal, into a flipflop reset at the beginning of the scanning by a synchronized signal from the television control unit, the output of the flip-flop being sent to said gate circuit, the output signal from which indicates the presence of pinholes or edge cracks.

In addition to this method, the inventors have developed a method for improving the sensitivity of the apparatus for the detection of pinholes or edge cracks, according to which, in the above method, the amplifying rate of the scanning signal is changed upon detection of an output from said flip-flop output. More particularly, to improve the sensitivity, the amplification factor is lowered by the output of the flip-flop when it is reset by the synchronizing signal at the beginning of the scanning, and is returned to the original level by the output of the flip-flop when it is set by a signal for the edge of the article being inspected.

An object of the present invention is to provide a method and apparatus for detecting pinholes and edge cracks in such thin articles as paper, rubber sheet and metal sheets, according to which pinholes and edge cracks in such articles can be detected comparatively simply, accurately and swiftly, particularly those on the side edges of such articles which cannot be detected by the conventional method.

Another object of the present invention is to provide a method and apparatus for detecting defects in the side edges of bands, by which pinholes in such thin bands which are moving or swaying at high speed, or such defects in the side ends of such bands as rugged edges and projections are detected swiftly and without fail.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional view of a conventional apparatus for detecting pinholes.

FIG. 2 is a schematic view of an apparatus for carrying out the method of the present invention.

FIG. 3 is a schematic view of a modified apparatus for carrying out a modified method of the present invention.

FIG. 4 is a schematic view illustrating the detecting method of the present invention.

FIG. 5 shows a series of pulses of the video signal produced by the method of the present invention.

FIG. 6 is a block diagram of a circuit for the practice of the method of the present invention.

FIG. 7 is a block diagram of a circuit for carrying out an improved method from the method carried out by the circuit which is shown in FIG. 6.

FIG. S is a schematic view of another scanning unit according to the present invention.

FIG. 9 is a schematic view of the snaking of a long, narrow strip under examination.

FIG. 10 is a diagram of the area scanned by the apparatus of the present invention.

FIG. 11 is a block diagram of the apparatus of the present invention.

FIG. 12 is a diagram of the scanning process carried out by the apparatus of FIG. ll 1.

FIG. 13 is a diagram of the electric signal produced by the apparatus of FIG. 11.

FIG. 14 is a theoretical diagram of a process of removing defective signals from electronic signals produced by the apparatus of FIG. I 1.

FIG. 15 shows a diagram of another process of removing defective signals.

FIG. 16 is a diagram of an apparatus for carrying out another scanning process from that of FIG. Ill.

FIG. 17 is a block diagram of another apparatus than that of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 the article 1 to-be-examined such as a piece of tin-plate sheet has light from a source of light 2 cast on the surface thereof. A pinhole 3 is present in the tinplate sheet 1. The parts are contained in a dark box 4. Photoelectric elements 5 are positioned below the sheet 1 from which is issued electric signals when light 2 passing through the pinhole 3 strikes one of the elements 5. A movable light-leakage prevention mask 7 is pressed by a press 8 against the sides 6 and 6 of the tinplate sheet 1. An apparatus 9 is connected to the elements 5 for detecting an electric signal.

With this construction of the conventional apparatus, it is necessary to use a light-leakage prevention mask 7, as mentioned above, in order to prevent leakage of light issuing from the source 2 from the space between respective sides 6 and 6' of the tin-plate sheet 1 and respective side walls of the dark box 5 into the space on the back side of the tin-plate sheet. Because of use of the light-leakage prevention mask 7, the areas 1' along the edges of the tin-plate sheet 1 which are each about 2 to 8 mm wide constitute the dead zones, making it impossible to detect pinholes in these areas.

In FIG. 2 showing one embodiment of the apparatus of the present invention, the article 1 to-be-examined such as a piece of tin-plate sheet has light from a source of light 2 such as a fluorescent lamp directed thereon. A pinhole 3 is present in the tin-plate sheet 1. A television camera 10 is directed at the back side of the plate 1. A television control unit 1 1 is provided for the television camera 10 and an amplifier 12 is connected to the output of the camera 10 for amplifying the video signal issued by the television camera. A conventional Schmidt circuit 13 is connected to the amplifier 12 and a unit 14 is provided for indicating electric signals passing the Schmidt circuit 13, for example a counter. The television camera 10 has a scanning area Q.

In case light issued from the source 2 and passing through pinholes 3, is detected by the television camera 10, it is converted into pulse signals of higher level than the signals issued by the television camera 10; therefore, it is easy to detect such pulse signals, by the Schmidt circuit 13 after they have been amplified with the amplifier 12, as shown in the drawing, and indicate them numerically with the counter 14. If the intensity of light from the source is raised or light of a special wave length is used in the above case, there is no need at all for a dark box, making it easier to detect pinholes.

On the basis of the above idea, the inventors of the present invention have developed another method for detecting small pinholes on the side edges 1" of the tinplate sheet 1 even through the tin-plate sheet 1 is moving. This process is illustrated in FIG. 3.

In FIG. 3 showing one embodiment of the apparatus for practicing the method of the present invention, a piece of tin-plate sheet 1 has light from a fluorescent lamp 2 having a light pattern wider than the width of the tin-plate sheet 1 directed onto it. Television cameras 10 and 10' are positioned with their longitudinal center lines directed toward the opposite edges 1" of the tin plate 1 at right angles to the plate surface and with their focal points adjusted to the edges of the tinplate 1. Light 15 is directed from the fluorescent lamp 2 to the surface of the tin-plate sheet, and light 16 from the lamp reaches the television cameras 10 and 10 directly without interruption by the tin-plate sheet 1.

As this embodiment is mainly for the purpose of detecting pinholes in the area along the edge 1 of the tinplate sheet 1, two television cameras 10 and 10 were provided.

The following is a detailed description of the detection method using the apparatus of FIG. 3 according to the present invention.

In FIG. 4, 17 indicates the scanning area of the television cameras 10 and 10' (only the area for one camera is shown) and 18 indicates a pinhole in the tinplate sheet 1; 19 indicates the prescribed position of the transverse centerlines; 20 is an arrow indicating the direction of movement of the tin-plate sheet. In this figure, light 16 and light 15 are directed into the television camera 10, respectively, from the left side of the edge 1 of the tinplate sheet 1 and from the right side through the pinhole 18.

Therefore, the video signals produced by horizontal scanning by the television camera 10 along the line 19 is the pulse series 21, as shown in FIG. 5. That is, the pulse 22 is produced by the light 16 and the pulse 23 by the light 15. Therefore, as can be seen from FIGS. 4, 5 and 6, the detection of pinholes can be accomplished by clipping at the set level 26 of the Schmidt circuit 13, say, as high as half the width of the pulse, and by taking the pulse 22 and the pulse 23 out separately.

In FIG. 5, 27 indicates the zero level of the signals; 24 and 24 indicate synchronized signal pulses issued from the television control unit 31 shown in FIG. 6. Scanning progresses in the direction of the arrow 28. While the control unit, which is a television system component, is capable of generating both horizontal and vertical synchronizing signals, only horizontal synchronizing signal pulses are utilized in this embodiment. For easier understanding, this will be explained below, together with the block diagram of FIG. 6.

In FIG. 6, 10 indicates the television camera; 12 indicates the amplifier for the video signals; and 13 indicates the Schmidt circuit for the amplified video signals. A wave-like reverser 29 is connected to the Schmidt circuit and one input of flip-flop 30 is connected to the wave form reverser. The television control unit 31 is connected to one input of the flip-flop and a gate circuit 32 is connected to the output of the flip-flop. The gate circuit 32 is also connected directly to the Schmidt circuit. 14 indicates the pinhole indication unit, such as a counter. When using such apparatus, video signals issued by the television camera 10 are amplified by the amplifier l2, clipped by the Schmidt circuit at the prescribed level, and set to the gate circuit 32. However, with only this kind of signal, the gate circuit 32 does not gate, and therefore no signals are conveyed to the counter 14. The branch circuit from the Schmidt circuit is used to send said video signals to the flip-flop 30 through the wave form reverser 29. The flip-flop 30 has setting input terminal S and resetting input terminal R, each of which actuates the flip-flop by the rise of an input pulse. If said flip-flop 30 has been reset to the 0" state with the rise of the synchronized pulse 24 sent from the television control unit 31, the flip-flop 30 will be set to the 1 state by the rise of the pulse 22 in said pulse series 21 (in this case, because the pulse 22 is inverted by the wave form reverser 29, so that it is the rise of inverted pulse 22 which sets the flip-flop 30). Only after this is the I state output of the flip-flop 30 conveyed to the gate circuit. Therefore, the gate circuit 32 does not pass the signal of the pulse 22 shown in FIG. 5, and thus only the pulse 23 produced subsequently to the pulse 22, that is, the signal produced by the presence of a pinhole, is conducted to the pinhole indication unit 14. The situation is the same for a plurality of pulses 23. This is because without production of the synchronized pulse 24', the flip-flop will not be reset.

The wave-form reverser can be omitted by selective- Iy using the input and output terminals of the flip-flop. Also, on the basis of the abovementioned principle of the present invention, horizontal scanning by the television camera alone will do, no vertical scanning being necessary. It will be understood that use of a nonimage type video tube is more effective for this purpose. That is, if such a tube is used, continuous horizontal scanning can be carried out at a fixed position, making it possible to detect pinholes in the article 1 to be examined, while the article is moving at high speed.

Further to the above method, the inventors of the present invention have developed a further method for ensuring exactness in the practice of the method of the present invention as a result of their continued research and study of the present invention.

In this last mentioned method, at the instant when theflip-flop 30 is set by said pulse 22 to produce an output, as shown in FIG. 7, a television series sensitivity controller 33 is caused to amplify said output and video signal. The television series sensitivity controller 33 is connected between the I state output of the flip-flop 3t] and the amplifier 12 so as to raise the sensitivity. That is, the amplifying rate of the television output by the output of the flip-flop 30 when it is reset by the pulse 24 of the synchronized signal and set by the pulse 22. That is to say, the vertical fall of the pulse 22 shown in FIG. 5 marks the edge 16 of the tin-plate sheet, and therefore, increasing video-sensitivity after the vertical fall of the pulse 22 makes the detection of light 15 passing through small-sized pinholes easier.

In other words, the pulse 22 is the result of a great quantity of light which can be easily detected. Therefore, it is desirable in actual operation that until the edge of the tin-plate sheet I is reached during scanning, the detecting sensitivity should be held down, so that possible dispersion of light 16 will not prevent detection of pinholes in the vicinity of said edge 16. If the video sensitivity is too high, it might well be desirable to reduce it until the fall of the pulse 22 and arrange that the fall of the pulse 22 returns video to a normal level. This should be understood as a technique which is at the disposal of those who will practice the method of the present invention within the scope of its objects. In this case the output signal from the flip-flop can be used as the trigger for changing the amplifying rate, but in restoring the amplifying rate, a synchronized signal such as the pulse 24 shown in FIG. 5 can also be used.

The following is a description of the operation of a further embodiment of an apparatus for detecting such defects as rough edges and projections on the side edges of a band material, such as steel sheet strips, by using the method of the present invention.

According to this aspect of the present invention, the addition of a particular electric circuit to the above described apparatus makes more accurate the detection of rough edges and projections on steel sheet strips.

As explained in detail above, the present invention relates to a method for detecting pinholes by directing light onto the strip 1 from a source 2 above one surface of said strip, catching the direct light from the source as well as light passing through pinholes in said strip 1 by a television camera set on the opposite side of the strip from the source 2, such light being converted into signals, the signals being divided into edge signals and signals representing light which has passed through pinholes by means of a group of signal treating electronic circuits, thereby detecting pinholes in the strip.

However, it is also possible to detect such defects in the edges of steel sheet strips or other long, narrow strip pieces, such as rough edges and projections, by utilizing edge signals obtained by the above method of the present invention. In order to obtain such edge signals, a known rotary mirror as shown in FIG. 8, that is, the flying image system, can be used in place of said television camera 10. In that figure, 1 designates the strip, 2 designates the source on the back side of said strip; 34 designates a group of signal treating electronic circuits; 35 designates a rotary mirror; 36 designates a diaphragm; 37 designates a light receiving cylinder containing photoelectric elements; and 38 designates light issued from the source. By using such apparatus, edge signals can be detected without difficulty.

As shown in FIG. 10, any apparatus can be used, if it covers the edge 39 of the strip 1 with its scanning area 40, and can convert light signals into electric signals while constantly scanning along the scanning line 41.

42 designates a pinhole, and 43 a rough edge, both being defects in the edge of the strip.

In FIG. 11 showing a block diagram of an embodiment of the apparatus of the present invention for detecting defects in the edges of steel sheet strips, 1 designates the strip, 2 designates a source of light; 10 designates a television camera, preferably of the nonimage type, or any reflection means such as the flying image system as described above; an amplifier 45 is connected to the camera 10 for amplifying signals from the television camera 10; a slicer 46 is connected to the amplifier for slicing the electronic signals to a prescribed level. A reverser 47 is connected to the slicer for reversing electronic signals issued from said slicer 46, and a flip-flop circuit 48 has a setting input connected to the reverser for setting by resetting signals issued from the flip-flop to the 0" state, and has a reset input R connected to a control unit 49, so as to be reset to the 1" state by resetting signals issued from the control unit 49 of said television camera 10 (or from the rotary mirror 35, (not shown) of flying image system). A delay circuit 50 is connected to the output of the flip-flop for detaining said electric signals for one scanning cycle (hereafter called II-I), and a reverser 51 is connected to the delay circuit for reversing output signals from said delay circuit 50. A primary AND gate circuit is connected to the 0 state output of flip-flop 48 and has the gate terminal connected to the reverser 51 so that the gate is opened to pass signals when a signal is received from the flip-flop circuit and an output signal is received from the reverser 51. A secondary delay circuit 53 is connected to the primary gate circuit 52 for detecting signals from the primary AND gate circuit and delaying them for at time determined according to the size of the defects and the degree of snaking of the strip. An AND gate circuit 54 is connected to the primary gate circuit 52 and has the gate terminal connected to the secondary delay circuit 53, and gate circuit 54 is opened when it receives an on-signal from the primary AND gate circuit 52 and an on-signal from said delay circuit. An indicator 55 is connected to the secondary gate circuit 54 to indicate output signals; that is, rough edge indication signals from the secondary AND gate circuit.

The operation process of the apparatus of FIG. 11 is as follows. The scanning by the television camera over different points on the edge 1a, lb and lj of the strip 1 of FIG. 9 is schematically shown in FIG. 12. In FIG. 12, as well as in FIG. 9, the snaking of the strip is exaggerated. At the edge point In, scanning is along the line A1, light coming past the edge in the distance between a] and a2 from the source 2, and no light passing the strip 1 in the distance between a2 and a3, the light being interrupted by the strip 1. This produces an electric signal, that is, an output signal from the flipflop circuit 48 through the amplifier 45, the slicer 46 and the reverser 47, which is shown as signal wave A2 in FIG. 13, in which the vertical axis represents voltage, that is, whether or not light is detected, and the horizontal axis represents scanning time, that is, scanning position. For ease of explanation, the flip-flop 4 8 is used in the reverse way from the use in pinhole detection; that is, the output used is that when the flipflop is in the fa state, the state opposite the 1 state set by the input from the reverser 47. When the flipflop 3f. reset with with a resetting signal from the controi t 49 just before the starting point of scanning at. the output from the 0" state is in the form of we which has a vertical portion at a4 corresponding to the starting point 21 of scanning and a vertical portion at corresponding to the edge point a2. Simiia 'iy, in the scanning of the edge points 1b and llj, signal waves and J21 will be obtained, if there are no rough edges at b2 and j2 in FIG. 13; and if there are such rough edges, as at defects 3a and 3b, the signal waves B22. and 322 are obtained.

Needless to say, scanning is repeated at the same position. According to the present invention, detection of defects is carried out so that as signals are obtained one after another by the thus repeated scanning, each video signal is compared with the previous one.

lVleanv-xhile, said signai A2 is divided into two parts,

one being fed directly into the primary AND gate circuit and the other being fed into the primary AND gate circuit 52 through the primary delay circuit 51) and the reverser 52. Then the next video signal, that is, B 21 or 822, is fed to the primary AND gate circuit 52. The signal B21 is that which is produced when there is no defect in the edge, and the strip 1 has snalted only in the left direction. At the same time, this signal B21 is put into the primary AND gate circuit 52, a reversed signal A3, shown in FIG. 14, which is produced by the delay by EH of the signal A2 obtained by the previous scanning is fed to the primary gate circuit. However, as cicarly shown in FIG. 16, there is no time when both signals together generate an on signal in FIG. 14 a positive voltage. and therefore, no output signal is produced at the primary AND gate circuit 52. Thus, when there is no defect in the edge, the snaking of the strip 1 in the left direction is not detected. In other words, such snaking does not influence the detecting operations. If there is a defect 3a in the edge, so the signal B22 is obtained, there is a time when both of the signals A3 and B22 together generate an on" signal in FIG. 14 a positive voltage, and therefore an output signal D for this time is produced in the primary AND gate circuit 52. That is to say, even if the strip 1 has snaked in the left direction, whatever defect is present can be detected accurately. It might be thought that the effect of the snaking of the strip in the left direction might offset the effect of the defect precluding the possibility of both signals being the same sign, therefore making it impossible to detect defects. However, any error due to such snaking in the detecting process can be avoided by raising the scanning pitch, i.e. the number of scannings per unit length of material in actual operation. As mentioned above, in the practice of the present invention, two succeeding video signals are compared. Therefore, if the scanning pitch is raised, the snaking of the strip during movement between scannings is very small relative to the depth of the defeet (corresponding to the distance between b2 and b3 in FIG. 12). After the primary AND gate circuit 52, said output signal D is again divided into two, one part being sent directly and the other through the delay circuit 53 to the secondary AND gate circuit 54. The delay circuit 53 is designed so as to delay signals for an appropriate time, say 1/50 H, taking into consideration the size of of the defect and the snaking of the strip 1. Therefore, there will be fed into the secondary AND gate circuit 54 the signal D and the signal E which is 1/50 H behind the former one. As a result, as shown in FIG. t4, there will be produced the signal F having a duration l/SO H shorter than the signal D, and signal F will be led into the signal indicator 55 as a defect indicating signal. By choosing an appropriate delay, for example, of 1/50 H, the defect indicating signals of that duration are not detected, and thus signals of that duration that are produced due to the snaking of the but by appear as if they were due to defects will be removed in this time duration and will not influence detecting operations.

FIG. 15 shows the case in which the scanning B1 of FIG. 12 was followed by the scanning II. The process of producing signals is omitted, as it is the same as mentioned above. In FIG. 15, the signal B33 is a signal obtained from the reverser 51 to be fed to the primary AND gate circuit 52; and the signal J22 is that which is obtained from the flip-flop iii to be fed directly to the primary AND gate circuit 52. As clearly understandable from this figure, because there is a time when both the signals B33 and .122 are the same sign, the output signal D1 is produced for this time in the primary AND gate circuit 52. In the same manner as described above, said signal is produced as an output signal from the secondary AND gate circuit 54, and a defect indicating signal is fed to the signal indicator 55. If there is no defeet in the edge l j, there is produced a signal like J21 shown in FIG. 13, but there is no time during which it is the same sign as the signal B33 shown in FIG. 15, so

that no output signal is produced in the primary AND gate circuit 52. That is to say, the snaking of the strip in the right direction does not affect detecting operations.

The above signal might be thought to be a rough indicating signal, even when there is no such defect in the edge, when the signal B21 of FIG. 13, which has been produced when there is no defect, is followed by the signal J21 obtained from the subsequent scanning, leaving a time in which both signals are the same sign. In actual operations, however, there will occur no such disturbance due to the snaking of the strip.

As described above in detail, such disturbance will occur only during the delay time of 1/50 II. If there is still a defect indicating signal to be produced by the simultaneous issue of the signals B21 and J 21, it will be produced only when the signal B21 has been obtained because of a projection on the edge. It will thus be understood that by the above method of the present invention, projections as well as rough edges can be detected according to the present invention. When the scanning speed of the scanning unit is too high in proportion to a slow speed of movement of the strip 1, or for other reason, the delay time in the delay circuit 50 can be made longer, not only for l scanning cycle, cut also any integral number of times longer than the above scanning cycle. That is to say, in actual operations, when the selection of qualified articles is the sole purpose, it is uneconomical to detect two signals for one rough spot or defect, even if it is very rough in proportion to the scanning pitch. Even for the purpose of determining the number of defects per unit length of the strip, operation of the system to have one defect cause production of more'than two defect indicating signals should be avoided. Therefore, the delay time should be set originally at l scanning cycle, and then, if necessary, should be extended to an integral number of times of the scanning cycle, depending on the purpose of detecting defects and the strip processing and examining processes. All the above-mentioned is within the scope of technology of the present invention.

Besides the above-mentioned apparatus which has the light source positioned above one surface of the article to be examined scans the article from below, another type of apparatus is possible which has the scanning unit as well as the light source on the same side of the article, as shown in FIG. 16. In this figure, l designates a strip; 2 designates the light source; designates a television camera. If there is an article having a high reflectionindex behind the article to be examined, that is, behind the strip 1, it can cause production of incorrect reflections. To overcome this, there can be placed behind the strip an article 56 having a low reflection index such as a black sheet. This, however, is not an indispensible condition. In FIG. 16, electric signals from the television camera 10 have a wave form the reverse of that shown in FIG. 13, making unnecessary the reverser 47 ahead of the flip-flop 48, as shown in the circuit diagram of FIG. 11. That is to say, a circuit as shown in FIG. 17 is sufficient in which figure the same number indicates the same unit as in FIG. 11. Also the treatment of the signal after the flipflop 48 is the same as in FIG. 11, and therefore, a

unnecessary. In summary, the signal wave forming circuits can be so arranged that electric signals put into description of the circuit of FIG. 17 and its operation is 6 the flip-flop 48 have the wave form as shown in FIG. 13. In addition, circuits can be added to improve the wave form of the signals. It should be understood that all of these arrangements are within the scope of technology of the present invention.

As mentioned above, the use of the method of the present invention makes it possible to swiftly and accurately detect such defects as rough edges and projections on the edges of long, narrow strip sheet moving continuously at high speed by using an apparatus having a comparatively simple construction, which contributes much to industries concerned with such technology as mentioned above.

We claim:

1. A method for detecting defects in sheet articles which comprises:

projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; scanning optically the other side surface on the other side of said article on a scanning line across the sheet article and outwardly beyond the edges of said sheet article in a direction perpendicular to the direction of movement of said sheet article for detecting light of a predetermined intensity passing the edge of said article; generating a signal each time during scanning light of a predetermined intensity is detected;

delaying the thus generated detection signal for a time which is an integral number of times of the scanning period;

combining a signal generated in a successive scanning with the delayed signal for producing a signal representing such defects as edge cracks and projections which are present at the edges of the sheet article;

delaying said signal representing such defects for a required length of time;

combining said signal representing such defects with said lastmentioned delayed signal for eliminating signals generated by negligible defects and generated by the snaking of the sheet article and leaving only signals representing defects of a magnitude which it is desired to detect; and

causing an indication means to operate in response to signals representing defects of a magnitude which it is desired to detect, thereby indicating the presence of such defects.

2. A method for detecting defects in sheet articles which comprises:

projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; scanning optically the said one surface of said article on a scanning line across the sheet article and outwardly beyond the edges of said sheet article in a direction perpendicular to the direction of movement of said sheet article for detecting light of a predetermined intensity reflected from said sheet article as compared to light which passes the edges of said article; generating a signal each time during scanning light of a predetermined intensity is detected;

delaying the thus generated detection signal for a time which is an integral number of times of the scanning period;

combining a signal generated in a successive scanning with the delayed signal for producing a signal representing such defects as edge cracks and projections which are present at the edges of the sheet article;

delaying said signal representing such defects for a required length of time;

combining said signal representing such defects with said lastmentioned delayed signal for eliminating signals generated by negligible defects and generated by the snaking of the sheet article and leaving only signals representing defects of a magnitude which it is desired to detect; and

causing an indication means to operate in response to signals representing defects of a magnitude which it is desired to detect, thereby indicating the presence of such defects.

3. An apparatus for detecting defects in sheet articles which comprises:

a light source for projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article;

a scanning means for scanning the surface on the other side of said sheet article on a scanning line perpendicular to the direction of movement of said sheet article from beyond the outside of said sheet article toward the center of said sheet article and for converting to electric signals light of a predetermined intensity from said source which passes the edges of said sheet article;

a wave shaping means coupled to said scanning means for shaping of output signals from said scanning means into a wave-like signal substantially consisting of rectangular pulse signals;

a pulse generating means coupled to said scanning means for generating a pulse at the starting point of said scanning;

a flip-flop means to which said wave shaping means and said pulse generating means are coupled for receiving output signals from said wave shaping means and said pulse generating means and for being set at the finish of the first rectangular output signal from said wave shaping means and for being reset by an output signal from said pulse generating means;

a primary time delay means coupled to said flip-flop means for receiving output signals from said flipflop means as input signals and for delaying said input signals for a time which is an integral number of times of the scanning period of said scanning means;

wave form reversing means coupled to said primary time delay means of the output signals from said primary time delay means;

a primary AND gate means coupled to said flip-flop means and said wave form reversing means for receiving output signals from said flip-flop means and from said wave form reversing means as input signals, and for being opened when output signals issued from said flip-flop means and from said wave form reversing means are on-signals, and for producing output signals representing defects such as edge cracks and projections on said sheet article;

a secondary time delay means coupled to said primary AND gate means for receiving output signals from said primary AND gate means and for delaying said output signals from said primary AND gate means for a time depending on the size of defects to be detected and for offsetting the effect of the snaking of said sheet article;

a secondary AND gate means coupled to said secondary time delay means and to said primary AND gate means for receiving output signals from said primary AND gate means and from said secondary time delay means for being opened when output signal issued from said primary AND gate means and from said secondary time delay means are onsignals, and for eliminating from the output signals of said primary AND gate means those signals representing defects of a size less than those desired to be detected and those signals caused by snaking of the sheet article; and

an indication means coupled to said secondary AND gate means and operated by output signals from said secondary AND gate means for indicating the presence of defects of the size to be detected.

4. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera having a non-storage type image pickup tube whereby the article can be scanned when the moving speed of said subject article is relatively high.

5. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera.

6. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera which performs only a horizontal scan.

7. An apparatus as claimed in claim 3 wherein said scanning means comprises a flying-image system including a rotary mirror, a diaphragm positioned to receive light from said mirror, and a light receiving cylinder containing photoelectric elements positioned to receive light from said diaphragm.

8. An apparatus as claimed in claim 3 wherein said scanning means comprises a flying-spot system including a rotary mirror, a diaphragm positioned to receive light from said mirror, and a light receiving cylinder containing photoelectric elements positioned to receive light from said diaphragm.

9. An apparatus for detecting defects in sheet articles which comprises:

a light source for projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article;

a scanning means for scanning the said surface on one side of the sheet article on a scanning line perpendicular to the direction of movement of said sheet article from beyond the outside edge of said sheet article toward the center of said sheet article and for converting to electric signals light of a predetermined intensity from said source which is reflected from said sheet article as compared to light which passes the edges of said sheet article;

a wave shaping means coupled to said scanning means for shaping of output signals from said scanning means into a wave-like signal substantially consisting of rectangular pulse signals;

a pulse generating means coupled to said scanning means for generating a pulse at the starting point of said scanning;

a flip-flop means to which said wave shaping means and said pulse generating means are coupled for receiving output signals from said wave shaping means and said pulse generating means and for being set at the finish of the first rectangular output signal from said wave shaping means and for being reset by an output signal from said pulse generating means;

a primary time delay means coupled to said flip-flop means for receiving output signals from said flipflop means as input signals and for delaying said input signals for a time which is an integral number of times of the scanning period of said scanning means;

wave form reversing means coupled to said primary time delay means for reversing the wave form of the output signals from said primary time delay means;

a primary AND gate means coupled to said flip-flop means and said wave form reversing means for receiving output signals from said flip-flop means and from said wave form reversing means as input signals and for being opened when output signals issued from said flip-flop means and from said wave form reversing means are on-signals, and for producing output signals representing defects such as edge cracks and projections on said sheet article;

a secondary time delay means coupled to said primary AND gate means for receiving output signals from said primary AND gate means and for delaying said output signals from said primary AND gate means for a time depending on the size of defects to be detected and for off-setting the effect of the shaking of said sheet article;

a secondary AND gate means coupled to said secondary time delay means and to said primary AND gate means for receiving output signals from said primary AND gate means and from said secondary time delay means for being opened when the output signal issued from said primary AND gate means and from said secondary time delay means are on-signals, and for eliminating from the output signals of said primary AND gate means those signals less than those desired to be detected and those signals caused by snaking of the sheet article; and

an indication means coupled to said secondary AND gate means and operated by output signals from said secondary AND gate means for indicating the presence of defects of the size to be detected. 

1. A method for detecting defects in sheet articles which comprises: projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; scanning optically the other side surface on the other side of said article on a scanning line across the sheet article and outwardly beyond the edges of said sheet article in a direction perpendicular to the direction of movement of said sheet article for detecting light of a predetermined intensity passing the edge of said article; generating a signal each time during scanning light of a predetermined intensity is detected; delaying the thus generated detection signal for a time which is an integral number of times of the scanning period; combining a signal generated in a successive scanning with the delayed signal for producing a signal representing such defects as edge cracks and projections which are present at the edges of the sheet article; delaying said signal representing such defects for a required length of time; combining said signal representing such defects with said lastmentioned delayed signal for eliminating signals generated by negligible defects and generated by the snaking of the sheet article and leaving only signals representing defects of a magnitude which it is desired to detect; and causing an indication means to operate in response to signals representing defects of a magnitude which it is desired to detect, thereby indicating the presence of such defects.
 1. A method for detecting defects in sheet articles which comprises: projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; scanning optically the other side surface on the other side of said article on a scanning line across the sheet article and outwardly beyond the edges of said sheet article in a direction perpendicular to the direction of movement of said sheet article for detecting light of a predetermined intensity passing the edge of said article; generating a signal each time during scanning light of a predetermined intensity is detected; delaying the thus generated detection signal for a time which is an integral number of times of the scanning period; combining a signal generated in a successive scanning with the delayed signal for producing a signal representing such defects as edge cracks and projections which are present at the edges of the sheet article; delaying said signal representing such defects for a required length of time; combining said signal representing such defects with said lastmentioned delayed signal for eliminating signals generated by negligible defects and generated by the snaking of the sheet article and leaving only signals representing defects of a magnitude which it is desired to detect; and causing an indication means to operate in response to signals representing defects of a magnitude which it is desired to detect, thereby indicating the presence of such defects.
 2. A method for detecting defects in sheet articles which comprises: projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; scanning optically the said one surface of said article on a scanning line across the sheet article and outwardly beyond the edges of said sheet article in a direction perpendicular to the direction of movement of said sheet article for detecting light of a predetermined intensity reflected from said sheet article as compared to light which passes the edges of said article; generating a signal each time during scanning light of a predetermined intensity is detected; delaying the thus generated detection signal for a time which is an integral number of times of the scanning period; combining a signal generated in a successive scanning with the delayed signal for producing a signal representing such defects as edge cracks and projections which are present at the edges of the sheet article; delaying said signal representing such defects for a required length of time; combining said signal representing such defects with said lastmentioned delayed signal for eliminating signals generated by negligible defects and generated by the snaking of the sheet article and leaving only signals representing defects of a magnitude which it is desired to detect; and causing an indication means to operate in response to signals representing defects of a magnitude which it is desired to detect, thereby indicating the presence of such defects.
 3. An apparatus for detecting defects in sheet articles which comprises: a light source for projecting light on the surface of one side of a sheet article moving in a certain direction over a range greater than the width of said article; a scanning means for scanning the surface on the other side of said sheet article on a scanning line perpendicular to the direction of movement of said sheet article from beyond the outside of said sheet article toward the center of said sheet article and for converting to electric signals light of a predetermined intensity from said source which passes the edges of said sheet article; a wave shaping means coupled to said scanning means for shaping of output signals from said scanning means into a wave-like signal substantially consisting of rectangular pulse signals; a pulse generating means coupled to said scanning means for generating a pulse at the starting point of said scanning; a flip-flop means to which said wave shaping means and said pulse generating means are coupled for receiving output signals from said wave shaping means and said pulse generating means and for being set at the finish of the first rectangular output signal from said wave shaping means and for being reset by an output signal from said pulse generating means; a primary time delay means coupled to said flip-flop means for receiving output signals from said flip-flop means as input signals and for delaying said input signals for a time which is an integral number of times of the scanning period of said scanning means; wave form reversing means coupled to said primary time delay means of the output signals from said primary time delay means; a primary AND gate means coupled to said flip-flop means and said wave form reversing means for receiving output signals from said flip-flop means and from said wave form reversing means as input signals, and for being opened when output signals issued from said flip-flop means and from said wave form reversing means are on-signals, and for producing output signals representing defects such as edge cracks and projections on said sheet article; a secondary time delay means coupled to said primary AND gate means for receiving output signals from said primary AND gate means and for delaying said output signals from said primary AND gate means for a time depending on the size of defects to be detected and for offsetting the effect of the snaking of said sheet article; a secondary AND gate means coupled to said secondary time delay means and to said primary AND gate means for receiving output signals from said primary AND gate means and from said secondary time delay means for being opened when output signal issued from said primary AND gate means and from said secondary time delay means are on-signals, and for eliminating from the output signals of said primary AND gate means those signals representing defects of a size less than those desired to be detected and those signals caused by snaking of the sheet article; and an indication means coupled to said secondary AND gate means and operated by output signals from said secondary AND gate means for indicating the presence of defects of the size to be detected.
 4. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera having a non-storage type image pickup tube whereby the article can be scanned when the moving speed of said subject article is relatively high.
 5. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera.
 6. An apparatus as claimed in claim 3 wherein said scanning means comprises a television camera which performs only a horizontal scan.
 7. An apparatus as claimed in claim 3 wherein said scanning means comprises a flying-image system including a rotary mirror, a diaphragm positioned to receive light from said mirror, and a light receiving cylinder conTaining photoelectric elements positioned to receive light from said diaphragm.
 8. An apparatus as claimed in claim 3 wherein said scanning means comprises a flying-spot system including a rotary mirror, a diaphragm positioned to receive light from said mirror, and a light receiving cylinder containing photoelectric elements positioned to receive light from said diaphragm. 